1. Field of the Invention
The present invention relates to a outer ring press fitted in a housing and having a track surface on its inner diameter surface, a drawn cup needle roller bearing, a drawn cup needle roller bearing structured body, a piston pin supporting structure of an engine, a crankshaft supporting structure of an engine, and a 2-cycle engine comprising the above outer ring.
2. Description of the Background Art
A 2-cycle engine having small capacity is used in a utility engine of a bush cutter and the like. A technique regarding the 2-cycle engine is disclosed in Japanese Unexamined Patent Publication No. 7-332371.
FIG. 14 is a longitudinal sectional view showing a 2-cycle engine in which roller bearings are used at the small end part and large end part of a connecting rod con-rod). Referring to FIG. 14, the 2-cycle engine comprises a crankshaft 83 outputting rotary motion, a piston 85 moving in a linear line back and forth, and a con-rod 84 connecting the crankshaft 83 to the piston 85 and converting the linear reciprocating motion to the rotary motion. The crankshaft 83 rotates around a rotation center shaft 90 and keeps a rotation balance with a balance weight 91.
The mixed gas of gasoline and lubricant oil is sent from an inlet 87 to a crank chamber 82 and then led to a combustion chamber 89 arranged at the upper part of a cylinder 81 according to the vertical motion of the piston 85. The exhaust gas is discharged from an exhaust hole 88.
The con-rod 84 comprises a large end part 93 at the lower part of a linear rod and a small end part 94 at the upper part thereof. The crankshaft 83 is rotatably supported at the large end part 93 of the con-rod 84 through a roller bearing 86 mounted in an inner diameter hole, and a piston pin 92 connecting the piston 85 to the con-rod 84 is rotatably supported by a roller bearing 86 mounted in an inner diameter hole.
As the roller bearings 86 mounted in the inner diameter holes provided at the small end part and the large end part of the con-rod 84 to support the piston pin 92 and the crankshaft 83, a drawn cup needle roller bearing that can receive high load in spite of its small projected area and highly rigid is used. Here, the drawn cup needle roller bearing comprises a outer ring formed of a steel plate processed by drawing, a plurality of rollers and a retainer. The retainer comprises pockets for holding the rollers and the interval of the rollers is retained by a column part positioned between the pockets.
Here, one manufacturing method of the retainer contained in the above drawn cup needle roller bearing will be briefly described hereinafter. First, a band steel that is the material of the retainer is punched out to form a pocket having a size in which the roller can be held. Then, it is pressed into a V-shaped form in section at a pressing step. Then, it is cut to the circumferential length of the retainer, and the cut band steel is bent into a cylindrical shape and the end faces of the bent band steel are connected by welding and the like. Then, it is heat treated, whereby the retainer is completed.
Here, when the band steel is pressed so that its sectional configuration becomes V shape, since its height in the diameter direction can be largely ensured, the following effect is provided. FIGS. 15A and 15B are sectional views showing the cut band steel in the diameter direction after the pressing process before and after it is bent into the cylindrical shape. Since the interval of column parts 106 on the side of an inner diameter surface 112 before a retainer 104 is bent into the cylindrical shape (FIG. 15A) becomes small after the retainer 104 is bent into the cylindrical shape (FIG. 15B), a roller 103 held in the pocket is prevented from falling off toward the side of the inner diameter surface 112. In this case, the roller 103 may be prevented from escaping toward the side of an outer diameter surface 111 by providing a roller escape preventing part at the column part 106 on the side of the outer diameter surface 111.
In addition, FIG. 16 is a view showing a state in which the retainer 104 retaining the roller 103 is incorporated in a outer ring 102 and a shaft 101. By performing the pressing process so that its sectional configuration becomes V shape, the roller 103 can be guided in the vicinity of a PCD (Pitch Circle Diameter) 105 in which the roller 103 can roll most stably when guided.
In addition, a retainer of a roller bearing having the same configuration as that of the retainer manufactured by the above steps is disclosed in Japanese Unexamined Patent Publication No. 2005-98368.
A description will be made of a method for measuring the precision of the outer ring 102 contained in the above drawn cup needle roller bearing hereinafter. The outer ring 102 has a track surface on which the roller rolls, at its cylindrical inner diameter surface 119. Regarding the track surface of the outer ring 102, since it is necessary that the roller can roll stably, high dimensional precision is required.
When the precision of the track surface of the outer ring 102 in which the high dimensional precision is required is measured, a variation in thickness dimension in the circumferential direction, that is, a variation in thickness of the cylindrical part of the outer ring 102 has been measured. FIG. 17 is a view showing a state when the variation in thickness of the cylindrical part of the outer ring 102 is measured in this case. Referring to FIG. 17, the outer ring 102 has a track surface on which the roller rolls, on the side of the inner diameter surface 119 of its cylindrical part 116. Here, the variation in thickness of the cylindrical part 116 is measured such that while an outer diameter surface 118 is pressed with a reference member 117 at the position shown by an arrow X or Y in FIG. 17 and the corresponding inner diameter surface 119 is pressed with a gauge terminal, the outer ring 102 is rotated.
In addition, a drawn cup needle roller bearing comprising a outer ring having a track surface on its inner diameter surface, in which a thickness difference is provided at a cylindrical part is disclosed in Japanese Unexamined Patent Publication No. 2002-235753.
According to the method of measuring the precision of the above outer ring contained in the drawn cup needle roller bearing, when the thickness of the cylindrical part is measured, the variation in thickness of the cylindrical part 116, that is, a difference in thickness in the circumferential direction is measured. However, this is not necessarily optimal as a precision parameter for evaluating whether the roller can roll stably. Especially, since the cylindrical part 116 of the outer ring 102 is relatively thin, and it could be deformed at a heat treatment and the like, it is necessary to measure the configuration after press fitted.
In this case, while the outer ring is press fitted in an inner diameter hole provided in a reference ring having a reference surface for parallelism and the like, the generatrix configuration of the inner diameter surface of the outer ring is measured and this is to be set to the precision parameter. However, when the generatrix configuration is set to the precision parameter as it is, since the generatrix configuration is measured including a part other than the surface on which the roller rolls, it cannot be correctly evaluated whether the roller can roll stably or not.
Meanwhile, among the above manufacturing steps of the retainer, at the pocket punching-out step, the blade of a punch is pressed against the material of the retainer along a pocket configuration to punch out the pocket. In this case, a sheared surface and a fractured surface are generated in the side wall surface of the pocket, that is, the side wall surface of the column part positioned between the pockets. The sheared surface is a smooth surface punched out with the edge of the blade of the punch and the like. Meanwhile, the fractured surface is a coarse surface fractured by the material pressed and punched out with the blade edge.
Here, when the pocket is punched out from the side that becomes the inner diameter surface when the retainer is bent into the cylindrical shape at the pocket punching-out step, the fractured surface is positioned in the side wall surface of the column part on the side of the outer diameter surface.
FIG. 18 is a sectional view showing the retainer 104 in the diameter direction in this case. FIG. 19 is a sectional view showing the retainer 104 in the axial direction in this case. In FIG. 19, the part shown by a dotted line designates the roller 103 retained in the pocket of the retainer 104, and a dashed line designates the PCD 105. Referring to FIGS. 18 and 19, when the pocket is punched out from the direction shown by an arrow Z in the drawing that becomes the inner diameter surface 112, a sheared surface 108 is positioned on the side of the inner diameter surface 112 of a side wall surface 110, and a fractured surface 109 is positioned on the side of the outer diameter surface 111 of the side wall surface 110. Here, since the retainer 104 is pressed into the V shape, when it retains the roller 103, the fractured surface 109 is positioned at the center part of the side wall surface 110 in the vicinity of the PCD 105 and the sheared surface 108 is positioned at the end of the side wall surface 110 in the vicinity of the PCD 105.
A configuration curve 114 of the side wall surface 110 at the PCD 105 in this case is shown in FIG. 20 together with an outline 113 of the roller 103. Referring to FIG. 20, in the side wall surface 110, the center part is the fractured surface 109 and the end is the sheared surface 108. In this case, the configuration line 114 is recessed at the center part with respect to the outline 113, so that the roller 103 is in contact with the sheared surface 108 at the end of the side wall surface 110 when guided.
However, since the end of the roller 103 is chamfered and the end of the side wall surface 110 does not follow the outline 113 of the roller 103, the roller cannot be appropriately in contact with it, so that the roller 103 cannot be guided stably.
In the drawn cup needle roller bearing comprising the above retainer and outer ring, the roller cannot roll stably. In addition, when the above drawn cup needle roller bearing is used in a piston pin supporting structure of an engine and the like, the roller is skewed and seizing could be generated.